Adsorption mechanism of mixed salicylhydroxamic acid and tributyl phosphate collectors in fine cassiterite electro-flotation system

Abstract

Two reagents including salicylhydroxamic acid (SHA) and tributyl phosphate (TBP) were tested as collectors either separately or together for electro-flotation of fine cassiterite (<10 μm). Subsequently, the flotation mechanism of the fine cassiterite was investigated by adsorbance determination, electrophoretic mobility measurements and Fourier transform infra-red (FT-IR) spectrum checking. Results of the flotation experiments show that with SHA as a collector, the collecting performance is remarkably impacted by the pulp pH value as the floatability of cassiterite varies sharply when the pH changes, and flotation with SHA gives distinct maximum at about pH 6.5. Additionally, the floatability of cassiterite is determined by using SHA and TBP as collectors. The range of pulp pH for good floatability is broadened in the presence of TBP as auxiliary collector, and the utilization of TBP improves the recovery of cassiterite modestly. Moreover, the optimum pH value for cassiterite flotation is associated with adsorbance. The results of FT-IR spectrum and the electrophoretic mobility measurements indicate that the adsorption interaction between the collectors and the cassiterite is dominantly a kind of chemical bonding in the form of one or two cycle chelate rings due to the coordination of carbonyl group, hydroxamate and P=O group to the metal tin atoms, where the oxygen atoms contained in carbonyl group, hydroxamate and P=O group of the polar groups have the stereo conditions to form five-membered rings. In addition, the adsorption interactions of SHA and TBP on the surfaces of cassiterite are also dominated by means of hydrogen bonds.